Polymeric films are used in a wide variety of applications. Multilayer polymeric optical films are widely used for various purposes, including as mirrors and polarizers. These films often have extremely high reflectivity, while being lightweight and resistant to breakage. Exemplary applications for these films include compact electronic displays, including liquid crystal displays (LCDs) placed in mobile telephones, personal data assistants, computers, televisions and other devices.
One type of polymer that is useful in creating polarizer or mirror films is a polyester. One example of a polyester-based polarizer includes a stack of polyester layers of differing composition. A polyester is prepared by reactions of one or more different dicarboxylate monomers (e.g., compounds with two or more carboxylic acid or ester functional groups) with one or more different glycol monomers (e.g., compounds with two or more hydroxy functional groups). One example of a polyester useful in multilayer optical films is polyethylene naphthalate (PEN) which can be made, for example, by reactions of naphthalene dicarboxylic acid (or ester) with ethylene glycol.